Electrostatic solitary structures in non‐thermal plasmas

Solitary electrostatic structures involving density depletions have been observed in the upper ionosphere by the Freja satellite [ Dovner et al. , 1994]. If these are interpreted as ion sound solitons, the difficulty arises that the standard Korteweg‐de Vries description predicts structures with enhanced rather than depleted density. Here we show that the presence of non‐thermal electrons may change the nature of ion sound solitary structures and allow the existence of structures very like those observed.